Avalanche Forecast for Friday, March 6, 2020
This information was published 03/06/2020 at 7:05 AM.
The Bottom Line
- Hard slabs of wind deposited snow make up today’s avalanche problem. Triggering one of these wind slabs is unlikely.
- Sheltered terrain may harbor small pockets of softer snow could produce a small avalanche; a good reminder that Low avalanche danger does not mean no danger.
- A chance of up to 2” of snow this afternoon on lighter wind could make small new wind slabs. Forecasts seem to agree it will be less than 2”.
- Expect to encounter areas that have been stripped of all new snow and have a refrozen crust as exposed surface. This refrozen crust, and even hard wind slabs, present the possibility of a long, sliding fall. Crampons, an ice axe, and sharp ski edges can help mitigate this sort of fall.
- Avalanche danger is LOW today as avalanches are unlikely.
Yesterday, 1” of snow from the tail end of Wednesday’s snowstorm fell on the summit, though this arrived pre-dawn when the wind was raging above 90mph from the WNW. Wind speeds diminished through the day, from 80mph in the morning to about 20mph at midnight from the W. Temperatures remained in the teens F.
Today, current wind from the SW at 20mph should shift slowly through S, E and eventually get to NE by afternoon. Speeds will range from calm to 20mph. Some developing clouds may produce up to 2” of snow this afternoon, though likely less. Temperature on the summit will rise into the teens F.
Tomorrow, the summit will likely wake up to new snow, possibly up to 4” combined this afternoon and overnight, though it seems likely under 1” and localized in higher terrain. Wind will increase overnight tonight and be from the N 50-70mph tomorrow, shifting to the NW. Skies will start clear with clouds developing through the day.
Primary Avalanche Problem – Wind Slab
Observations from the field yesterday reported unreactive wind slabs on easterly aspects. These wind slabs formed on Wednesday when wind speed averaged 86mph and gusted to 133mph. In exposed terrain, these wind slabs will be thick, hard, and unlikely to avalanche. Large buttresses, cliffs, or trees that offer a break from wind may provide places that have softer snow which could act as an isolated pocket; skiers in Huntington yesterday who found this soft snow tucked under Pinnacle buttress reported good stability in the softer snow. If you find yourself going from wind slab deserving of crampons to good skiing, you’ve found a pocket of possibly unstable snow.
What is a Windslab Avalanche?
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
The calendar and weather is moving toward spring, but our snowpack is still mid-winter. As days get longer with more sunshine, our snowpack can change dramatically in the course of hours. Now that the sun is higher in the sky, southerly aspects can warm quickly, and then refreeze even faster. Today’s weather should stay cold and dry. Spring time also brings about the season where many people start looking at the steeper, more technical ski lines or ski descents that require effort to access. These can have shallower snowpacks, very steep pitches, and perhaps have not avalanched recently. The avalanche in Escape Hatch last week proved that the faceting that folks are finding in the snowpack can produce bigger avalanches. In places that have shallower snowpacks due to terrain, particularly with rocks that produce thin spots or slopes that have not avalanched recently, this faceting may come into play. Continuing to assess the snowpack you plan to travel in will lead to safer decision-making as we are a long way off from our isothermal, spring snowpack.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. New snow from the week will provide good turns with some scoured sections.
Details on daily snowfall totals, precipitation type, total depth of snow and other information can be found on our page devoted to snow study plot data. Click here to check it out.
Recent snowpack and avalanche observations can be found here and on Instagram. Your observations help improve our forecast product. Please take a moment and submit a photo or two and a brief description of snow and avalanche information that you gather in the field.
Safe travel in avalanche terrain requires training and experience. This forecast is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
Avalanche danger may change when actual weather differs from the higher summits forecast.
For more information contact the US Forest Service Snow Rangers, AMC visitor services staff at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or seasonally at the Harvard Cabin (generally December 1 through March 31). The Mount Washington Ski Patrol is also available on spring weekends.
Posted 03/06/2020 at 7:05 AM.
USDA Forest Service
White Mountain National Forest